The present invention relates to a thermoplastic composition having a high flexural modulus and/or high heat deflection temperature and a method for producing the same.
Thermoplastic elastomers (TPEs) make up a unique class of plastics that combine the key processing properties of thermoplastics with many of the physical properties of thermoset rubbers. TPEs feature many of the positive physical attributes of vulcanized rubbers, such as low compression set and high flexibility, but can be processed using conventional thermoplastic fabrication techniques, like injection molding, extrusion and blow molding. TPEs can be broken down into five major classes. These classes include, but are not limited to, styrene block copolymers (SBCs), thermoplastic olefins or polyolefins (TPOs), thermoplastic vulcanizates (TPVs), thermoplastic polyurethanes, (TPUs), and thermoplastic copolyester elastomers (COPEs). Other types of TPEs include copolyamides and PVC blends. In general, TPOs are produced by blending a thermoplastic like polypropylene with an unvulcanized elastomer like EPDM. TPUs are generally reactor-based TPEs manufactured using either polyester or polyether polyol. COPEs are usually block copolymers comprising alternating hard and soft segments where the soft segment is usually an ether and the hard segment is an ester. TPVs are generally two-phase systems, continuous and dispersed, with a conventional rubber as the dispersed phase and a polyolefin thermoplastic as the continuous phase. The rubber phase in a TPV product is usually vulcanized during the manufacturing process.
Thermoplastic elastomers are useful in a variety of applications, including automotive parts, such as bumpers, dashboards, and other automotive parts where plastics are useful; consumer goods, such as in appliances, electronics and the like; sports equipment; and other areas where plastics are used. A broad range of chemicals have been evaluated as filler treatments or interfacial agents in filled polymers, in particular TPEs, to improve mechanical properties of the polymers. Use of these chemicals has been less than ideal in many cases. For example, certain currently used chemicals yield TPEs that have a low flexural modulus and a low impact resistance, i.e., the TPE is both flexible and brittle. Other commonly used additives result in TPEs with gain in tensile elongation but with little change or even a decrease in flexural modulus such that the resulting composites are more ductile and more flexible. Although the following discussion will focus generally on one class of TPEs, the TPOs, it should be understood by those of ordinary skill in the art that the discussion will apply generally to all classes of TPEs with similar behavioral characteristics.
Still other additives increase the flexural modulus and decrease the impact resistance of the TPOs, i.e., the TPOs become stiff and brittle. In fact, an increase in flexural modulus of TPO generally results in a decrease in impact resistance and vice versa. In many applications, it is desirable to increase the flexural modulus of a TPO while increasing or at least maintaining its impact resistance, i.e., stiff and strong TPOs are useful in many applications. Many chemical additives increase the flexural modulus of TPOs; however, they also decrease the impact resistance of TPOs, and therefore are generally inappropriate as flexural modulus modifying agents. In fact, this decrease in a TPO""s impact resistance prevents most of the chemical additives from being useful in many instances.
Another important characteristic of polymers and TPOs, in particular, is the heat deflection temperature. Heat deflection temperature is the temperature at which a standard test bar of the material being tested deflects a specified amount under a specified load. It is desirable that this temperature be high, indicating the ability to withstand high temperatures without deformation.
Therefore, there is a need for a flexural modulus modifying agent for TPOs which does not substantially decrease the impact resistance of TPOs. There is additionally a need for an agent that improves the heat deflection temperature of a polymer.
One embodiment of the present invention provides a mineral filled TPO (MFTPO) composition and a method for producing such composition, which comprises a polymer mixture, a mineral, and a flexural modulus modifying agent. The flexural modulus modifying agent significantly increases the flexural modulus of the MFTPO (relative to a similar MFTPO composition which lacks the flexural modulus modifying agent) and does not substantially affect the impact resistance of the MFTPO.
The polymer mixture comprises a first polymer, e.g., an elastomer including rubber, and a second polymer, e.g., plastic. Preferably, the first polymer is an elastomer selected from the group consisting of EPDM, EPR, and mixtures thereof. Preferably, the second polymer is a plastic selected from the group consisting of polypropylene including either polypropylene homopolymers or polypropylene copolymers, polyethylene, and mixtures thereof. The amount of first polymer present in the polymeric mixture depends on a particular application of the MFTPO; however, in general, the amount of first polymer in the polymeric mixture is from about 5% to about 55% by weight of the total weight of the MFTPO composition.
Minerals that are useful for the MFTPO composition of the present invention include talc, mica, clay, and mixtures thereof. Preferably, the mineral is talc. Typically, the amount of mineral present in the MFTPO composition of the present invention is from about 5% by weight to about 40% by weight of the total weight of the MFTPO composition.
Flexural modulus modifying agents which are useful in the MFTPO composition of the present invention include polysiloxanes, polyols, including but not limited to polyether polyols, glycols, fatty acids, including but not limited to stearic acid, fatty acid amines, fatty acid amides, alkyl or aryl sulfonates, fatty acid esters, in situ calcium stearate wax and mixtures thereof. Preferably, the flexural modulus modifying agent is a polysiloxane or an alkylsulfonate, more preferably an alkylated polysiloxane. Generally, the flexural modulus modifying agent is present in the amount ranging from about 0.1% by weight to about 5% by weight of the weight of the mineral, more preferably from about 0.25% by weight to about 2% by weight and more preferably from about 0.5% by weight to about 1% by weight, based on the weight of the mineral.
The flexural modulus modifying agent increases flexural modulus of the MFTPO composition by at least about 10% relative to the flexural modulus of a MFTPO composition which lacks the flexural modulus modifying agent, preferably from about 10% to about 80%. Moreover, the difference in impact strength between the MFTPO composition containing the flexural modulus modifying agent and the impact strength of a similar MFTPO composition without the flexural modulus modifying agent is about 10% or less.
Another embodiment of the present invention provides a method for producing the MFTPO described above. The method generally involves admixing the mineral, the flexural modulus modifying agent and the polymer resin mixture (i.e., a polymer mixture) to produce a blended mixture; and producing the MFTPO from the blended mixture. The mineral and the flexural modulus modifying agent may be dispersed in the polymer mixture by processes such as batch mixing in a Banbury type mixer or in a continuous operation such as a compounding extruder, and the like. The conditions corresponding to good compounding practice are generally sufficient. In any event, one skilled in the art can determine when sufficient compounding has been achieved without undue experimentation. In continuous compounding, utilizing twin screw extruders or similar devices, the sequencing can be conveniently accomplished by introducing the ingredients at suitable feedport locations in the extruder. While the flexural modulus modifying agent can be added anytime during the MFTPO production, in one particular aspect of the present invention, it is added to the mineral to produce a surface treated mineral which is then admixed with the polymer resin mixture to produce the blended mixture. The surface treated mineral can be dried, if required, prior to admixing it with the polymer resin mixture. In one particular aspect of the present invention, the MFTPO is produced by an extrusion process, preferably using a twin screw extrusion process. The resulting mixture is then injection molded.
Another embodiment of the present invention provides a mineral filled TPO (MFTPO) composition and a method for producing such composition, which comprises a polymer mixture, a mineral, and a heat deflection temperature modifying agent. The heat deflection temperature modifying agent significantly increases the heat deflection temperature of the MFTPO (relative to a similar MFTPO composition which lacks the heat deflection temperature modifying agent) and does not substantially affect the impact resistance of the MFTPO.
The polymer mixture comprises a first polymer, e.g., an elastomer including rubber, and a second polymer, e.g., plastic. Preferably, the first polymer is an elastomer selected from the group consisting of EPDM, EPR, and mixtures thereof. Preferably, the second polymer is a plastic selected from the group consisting of polypropylene including either polypropylene homopolymers or polypropylene copolymers, polyethylene, and mixtures thereof. The amount of first polymer present in the polymeric mixture depends on a particular application of the MFTPO; however, in general, the amount of first polymer in the polymeric mixture is from about 5% to about 55% by weight of the total weight of the MFTPO composition.
Minerals that are useful for the MFTPO composition of the present invention include talc, mica, clay, and mixtures thereof. Preferably, the mineral is talc. Typically, the amount of mineral present in the MFTPO composition of the present invention is from about 5% by weight to about 40% by weight of the total weight of the MFTPO composition.
Heat deflection temperature modifying agents which are useful in the MFTPO composition of the present invention include polysiloxanes, polyols, including but not limited to polyether polyols, glycols, fatty acids, including but not limited to stearic acids, fatty acid amines, fatty acid amides, alkyl or aryl sulfonates, fatty acid esters, in situ calcium stearate in wax and mixtures thereof. Preferably, the heat deflection temperature modifying agent is a polysiloxane or an alkylsulfonate, more preferably an alkylated polysiloxane. Generally, the heat deflection temperature modifying agent is present in the amount ranging from about 0.1% by weight to about 5% by weight of the total weight of the mineral, more preferably from about 0.25% by weight to about 2% by weight and more preferably from about 0.5% by weight to about 1% by weight, based on the weight of the mineral.
The heat deflection temperature modifying agent increases the heat deflection temperature of the MFTPO composition by at least about 3xc2x0 C. relative to the heat deflection temperature of a MFTPO composition which lacks the heat deflection temperature modifying agent, preferably by at least about 5xc2x0 C. and more preferably by at least about 10xc2x0 C. Preferably, the difference in impact strength between the MFTPO composition containing the heat deflection temperature modifying agent and the impact strength of a similar MFTPO composition without the heat deflection temperature modifying agent is about 10% or less.
Another embodiment of the present invention provides a method for producing the MFTPO described above. The method generally involves admixing the mineral, the heat deflection temperature modifying agent and the polymer resin mixture (i.e., a polymer mixture) to produce a blended mixture; and producing the MFTPO from the blended mixture. The mineral and the heat deflection temperature modifying agent may be dispersed in the polymer mixture by processes such as batch mixing in a Banbury type mixer or in a continuous operation such as a compounding extruder, and the like. The conditions corresponding to good compounding practice are generally sufficient. In any event, one skilled in the art can determine when sufficient compounding has been achieved without undue experimentation. In continuous compounding, utilizing twin screw extruders or similar devices, the sequencing can be conveniently accomplished by introducing the ingredients at suitable feedport locations in the extruder. While the heat deflection temperature modifying agent can be added anytime during the MFTPO production, in one particular aspect of the present invention, it is added to the mineral to produce a surface treated mineral that is then admixed with the polymer resin mixture to produce the blended mixture. The surface treated mineral can be dried, if required, prior to admixing it with the polymer resin mixture. In one particular aspect of the present invention, the MFTPO is produced by an extrusion process, preferably using a twin screw extrusion process. The resulting mixture is then injection molded.